Why is seawater a better conductor of electricity than water from a freshwater lake?
Sea water is a better conductor because it has dissolved and dissociated ions.
The conductivity of water depends on the concentration of dissolved ions in solution.
The units of conductivity are Siemens per metre S/m.
Deionised water by its nature has very few ions. Its conductivity is about
Sea water has a relatively large number of Sodium and Chloride ions and has a conductivity of around 5S/m. This is because the Sodium Chloride salt dissociates into ions.
Hence sea water is about a million times more conductive than fresh water.